This invention is related to the recovery and recycling of gases. More particularly, this invention is related to the recovery and recycling of helium of from about 30% to 70% by volume in the production of optical fibers from the draw tower cooling tubes of the production apparatus.
The present state of the art for optical fiber manufacturing generally starts with the production of a specially prepared glass rod or preform. The preform is processed in a fiber drawing station to produce the optical fiber. A specially prepared glass preform is fed into a furnace where the glass melts, forming a semi-liquid fiber. As the fiber falls through the air and through a heat exchanger (chiller) it cools and solidifies. Following cooling, the fiber is coated and spooled. The draw rate is controlled by the rate of cooling in the space between the furnace and the coating applicator. In order to increase the rate of cooling, a small amount of gas is often applied to the fiber heat exchanger. Helium is generally used as the gas in this heat exchanger because it provides a high heat transfer rate and is inert. The heat exchanger generally consists of an aluminum or stainless steel block bored for a minimum diameter to allow the fiber to travel through it. Helium or a mixture of helium and air or nitrogen is also fed into the cylindrical channel where it flows out one or both ends of the block into the surrounding atmosphere. Heat is dissipated from the glass fiber through the helium and, into the wall of the heat exchanger. The heat exchanger can have conductive metal fins to dissipate the heat from the heat exchanger metal surface or the heat exchanger can be manufactured with an additional water-jacketed cooling source.
Helium consumption during the optical fiber draw cooling process varies from a few standard liters per minute (slpm) of helium to several hundred standard liters per minute of helium per heat exchanger. The prior art has disclosed helium recovery from and recycle to fiber optic drawing. See, U.S. Pat. Nos. 5,377,491 and 5,452,583.
These prior art include the use of rotating or reciprocating compression equipment, analytical equipment and controls to recover and recycle helium to the fiber optic drawing station heat exchangers. The decision to utilize this type of recovery method is determined by the quantity of helium used per heat exchanger, the cost of helium as well as the cost to purchase, operate and maintain the recovery system. The ultimate question that the fiber optics producer must determine is whether it is economically beneficial to invest in drawing tower helium recovery technology on a site-specific basis.
Generally, for applications where very low volumes of helium are used in the drawing tower heat exchangers (5-50 slpm per heat exchanger), current recovery technologies may not be economically viable.
The objective of this invention is to provide optical fiber producers with a low cost option for helium recovery and recycle. This is achieved by providing a helium recovery system which will result in 30% to 70% recovery of helium from each heat exchanger unit, without the use of any moving parts such as compressors, vacuum pumps, control valves and without the need of analytical equipment.
The prior art primarily uses xe2x80x9conce through heliumxe2x80x9d to cool the fiber during the drawing process or are using helium recovery and recycle technology (at a substantially higher helium flow than the present invention) to cool the fiber.
The prior art generally utilizes moving parts such as compressors, vacuum pumps and control valves. It would be desirable to provide a helium recovery system that uses no moving parts.
It would be desirable to use an eductor to facilitate helium recovery in a small-scale fiber optic cable manufacturing process. The prior art eductors are commonly used for mixing, evacuating, draining, drying, and many other routine process applications. The motive stream can be almost any fluid, and it can be used to move a suction stream composed of gases, liquids, or powder-type solids. The discharge stream combines the motive stream and suction stream and in most applications is significantly different from either of them. In the proposed helium recovery and recycle application, all three streams are basically the same regarding composition and properties.
Some types of eductors have been known. For example, U.S. Pat. No. 5,836,745 discloses a fluid recovery apparatus and method using a motive force, which includes the use of an eductor for recovering fluid from a liquid formation. It discloses a liquid submersible pump for pumping fluid from the liquid formation. There is no teaching or suggestion in this art for the recovery of helium gas and or other rare gases and does not recover a liquid.
U.S. Pat. No. 4,613,412 discloses an evacuator system and process for an evaporative recovery system, which uses an eductor to create a partial vacuum in an evaporative waste recovery system. It uses a fluid as the motive to the eductor in order to evacuate concentrate and distillate from an evaporator. There is no teaching or suggestion in this art for recovering and recycling helium gas or other rare gases.
U.S. Pat. No. 4,115,235 discloses an apparatus for conveying a gas sample through an analyzer chamber. The prior art uses an eductive loop in conjunction with a convective loop to convey a gas sample through an analyzer. This art does not teach or suggest helium or other rare gases to recover a portion of the gas discharged from the eductor. There is no teaching or suggestion in this art for recovering helium or other rare gases, and recycling these gases back into the system for re-use.
U.S. Pat. No. 5,795,146 discloses a furnace chamber having eductor to enhance thermal processing. This art discloses a furnace for thermally processing product and includes one or more eductors. The eductor(s) provides for increased circulation of atmosphere within the furnace for heat transfer or outgassing purposes. This patent discloses an eductor to increase circulation within a furnace chamber but does not use the eductor to recover helium or other rare gases.
It is desirable in the art to provide for a fiber optic manufacturing process and system, which recovers and recycles helium and other rare gases at a lower cost than that associated with the present gas recovery and recycling technology.
It is desirable to provide such a process that requires no moving parts, requires no power, requires no rotating compression equipment, can be installed as part of the fiber producer""s existing heat exchanger supply piping, and requires little or no maintenance.
Further, it is desirable to provide an economical method and system for the fabrication, installation, operation and maintenance of this equipment, which is particularly beneficial to the small volume helium recovering and recycling users.
This invention is directed to a process for recovering helium. The process comprises a) passing a first gas containing helium to an eductor to produce a second gas; b) passing the second gas through a heat exchanger to produce a third gas; and c) recovering the third gas into the eductor to combine with the first gas.
In one embodiment, the second gas may pass through a cooler. The second gas and/or third gas may pass through a rotometer. The third gas may be split into a top portion and a bottom portion as it emerges from the heat exchanger, and the flow of both the top portion and the bottom portion as they emerge from the heat exchanger may be partially regulated by flow control means, for example, valves. Particulate removing devices such as filters may be used to remove particulate from the third gas prior to combining with the first gas in the eductor.
As used herein, the term eductor means a hydraulic device. It may consists of a nozzle and venturi throat, used to create a negative pressure (suction) by discharging a high pressure motive stream fluid through a nozzle as a concentric, high speed jet flowing past or through a suction stream inlet tube into a discharge chamber. The negative pressure generated thus inducing a positive draw of suction stream material through the inlet tube and into the discharge chamber.
As used herein, the term rotometer means a device for measuring gas flow. One example is a simple cylindrical apparatus through which air flows and the rate of flow is measured.